Nitrogen oxide compounds (NOX) are typically formed during combustion processes which entail high temperatures and other factors which make possible the chemical combination of nitrogen and oxygen. NOX is shown to be an irritant in small quantities and a potentially greater threat to human life in large quantities. NOX is also suspected of being a significant source of pollution to the environment. In industrial burner systems, particularly those of the type that operate above one million BTU's per hour with flame temperatures approaching 3500.degree. F., localized production of NOX can be prodigious.
Increasingly, environmental protection agencies and state governments are tightening down on the pollutants which are discharged from burner systems including those used in industrial furnaces. As these limits are reduced, including those for NOX and CO, it becomes more difficult for burner manufacturers and operators to meet these pollution standards.
In a conventional premix burner system, it is common to mix fuel and oxidant remote from the site of combustion in order to create a premix, which is then flowed to the burner. In the event of flashback, the quantity of premix downstream of the mixing site may potentially combust resulting in a detonation wave traveling backward from the combustion site. Such flashback poses a great safety risk to personnel and destructive potential to equipment. For this reason, such burner systems are typically limited to a premix firing rate on the order of ten million BTU's per hour.
In prior premix systems, noise and vibration increase as the fuel to oxidant ratio approaches stoichiometric. A coupling between the external heat transfer rate and the intrinsic reaction rate of a fully premixed mixture can occur. This phenomenon is referred to as a Rayleigh oscillation. It is responsible for the "motor boating" sound often heard when pilots are fired through long tubes. While this phenomenon is not a problem in itself, this oscillation can match the natural frequencies in a particular firing chamber or room. When this happens, the two bootstrap each other into a much louder and more violent sound or vibration. Such vibration also has potentially destructive consequences.